Summary
If you make 121,199,988 원 a year living in South Korea, you will be taxed 29,765,983 원. That means that your net pay will be 91,434,005 원 per year, or 7,619,500 원 per month. Your average tax rate is 24.6% and your marginal tax rate is 40.7%. This marginal tax rate means that your immediate additional income will be taxed at this rate. For instance, an increase of 100 원 in your salary will be taxed 40.69 원, hence, your net pay will only increase by 59.31 원.
Bonus Example
A 1,000 원 bonus will generate an extra 593 원 of net incomes. A 5,000 원 bonus will generate an extra 2,966 원 of net incomes.